The 15N and 13C solid state NMR study of intramolecular hydrogen bond in some Schiff's bases

Schiff Bases from TRIS and ortho‐Hydroxyarenecarbaldehydes: Structures and Tautomeric Equilibria in the Solid State and in Solution

“…[27,37,41] Like in the solid state, thermochromism induced by proton transfer can also be observed in solution. [42,43] Selected spectroscopic data have been collected in Table 2. Compounds 20 and 21 show tautomeric forms, which are different from those examined crystallographically.…”

Solid‐state NMR study of Schiff base derivatives of 2‐hydroxynaphthaldehyde. Deuterium isotope effects on 15N chemical shifts in the solid state

“…Alarcón et al adopted the value of 180 ppm as characteristic of the pure NH tautomer either in the solid state 20 or in solution for N-(2-hyroxynaphthylidene)arylamines. 23,24 For N-(2-hydroxynaphthylidene)-n-propylamine (1) ( Table 1), the position of the 13 C signal of the C-2 carbon suggests that in the solid state this compound exists in the NH form. This suggestion is in agreement with the x-ray data.…”

“…1,2 Hence the study of proton dynamics in crystalline Schiff bases is of interest from both theoretical and practical points of view. In this work, we undertook a study of the tautomerism of Schiff base derivatives of 2-hydroxynaphthaldehyde by means of 13 C and 15 N cross-polarization magic angle spinning (CP/MAS) NMR spectroscopy and the deuterium isotope effect on the 15 N chemical shift. The deuterium isotope effect on 15 N chemical shift is defined as the difference between chemical shifts, N(D) D υN(H) υN(D), where υN(H) and υN(D) are chemical shifts observed for the non-deuterated and deuterated sample, respectively.…”

“…The methods that allow the detection of proton dynamics in the hydrogen bridge in the solid state are very low-temperature 15 N CP/MAS NMR and measurement of the spin-lattice relaxation rate T 1 , applied by Inabe et al, for N,N 0 -di(2-hydroxynaphthylidene)-p-phenyldiamine (DNP). 11,18,19 The existence of a tautomeric equilibrium in some solid N-(2-hydroxynaphthylidene)-(p-R-anilines) at room temperature has been demonstrated by using the residual 13 C, 14 N dipolar coupling effect. 20 The aim of this work was to confirm the usefulness of deuterium isotope effect measurements on 15 N CP/MAS chemical shifts for the detection of proton dynamics in the solid state in the intramolecular hydrogen bond.…”

Deuterium isotope effects on 15N chemical shifts of double Schiff bases in the solid state and solution

“…A comparison of the results obtained for 4 and 5, in solution and in the solid state, confirms the interdependence of the two hydrogen bonds in double Schiff bases. 3,4 It is also worth noting that, contrary to the general observation, 1,20 the NH tautomers of 3 and 4 are better stabilized by interactions in CDCl 3 solution than in the solid state.…”